1. Field of the Invention
This invention relates to fluid control valves, and more particularly, to an annular metal seat for use with control valves used at relatively high temperatures.
2. Description of the Prior Art
Butterfly and other types of fluid control valves with annular resilient seals are well known and commonly used for controlling the flow of various fluids at ambient or moderate temperatures and modest pressures in a wide variety of industries. However, the materials which are used in the seals of these valves tend to flow or creep when the temperature is raised, causing the valves to leak and to be unsatisfactory for high temperature use.
There have been attempts to design and build valves having a cantilever type of resilient metal seals for use at temperatures up to 1000 degrees F., but in general these valves require precision machining of the seal and other parts of the valve which causes the valve to be quite expensive. When the valve is closed, the cantilever type of metal seal yields an amount which is determined by the stress applied by a flow control element which presses against the seal so the cantilever seal does not return to the original configuration. In addition, the cantilever type of metal seal reaches the maximum safe working stress of the seal material at a relatively low value of applied load. The low applied load permissible with the cantilever type of metal seal limits the force which can be transmitted between the seal and the flow control element to a value less than that required for optimum sealing. As a result, after they have been opened and closed a few times these expensive valves develop a relatively high rate of leakage which makes them somewhat less than satisfactory for many industrial applications. Other prior art high temperature valves use an annular ring type of metal valve seal which is loaded by the flow control element to produce a hoop stress in the ring. This ring type of metal seal also requires expensive precision machining of the seal. The hoop loaded ring type of valve seal is also affected by the stress of deforming the seal and has a relatively high rate of leakage.
What is desired is a fluid-control valve having a resilient metal valve seat that maintains a fluid-tight contact with the valve body and with the flow control element over a wide range of temperatures up to approximately 1000.degree. F. The valve seat should continue to maintain the same fluid-tight contact with the flow control element after the valve has been opened and closed many times. It is also desirable to provide a valve that is relatively simple and inexpensive to build, and having an inexpensive, easily-replaceable metal seal.